قُلْ مَا يَكُونُ لِي أَنْ أُبَدِّلَهُ مِنْ تِلْقَاءِ نَفْسِي إِنْ أَتَّبِعُ إِلَّا مَا يُوحَى إِلَيَّ
Say: It is not for me to change it on my own; I only follow what is revealed to me. (Yūnus 10:15)
The Prophet ﷺ follows and faithfully conveys revelation. Changing it according to private wishes is incompatible with his divine mission.
This provides a clear basis for the protected character of prophetic teaching.